Hi Citoyen,
I created an account just to respond to this!
Ok, so this has happened to me twice, in about 3 years of owning a 510. To add some detail, when you upload to Garmin or Strava, it can tell that you have done the pre-crash ride, (IE for me, the strava recording seems to start at about 30km and goes on to 110km, but shows a total distance of about 85km, which is the distance travelled after the crash), but can't recover the data pre-crash.
To prevent this, I am now deleting all my rides (not the records) about once a month, which both seems to stop the problem, and also makes the upload of new activities much faster. Since I literally NEVER look at old rides on the device itself anyway, this isn't really a hassle or inconvenience.
I don't, however, believe that there is a way to recover the pre-crash data.
Hope this helps!